First principles study on the electronic and optical properties of Al- and Si-doped ZnO with GGA and mBJ approximations

Optical properties of ZnO doped with Silicon and Aluminum were studied by first principle calculations using the density functional theory. The optical absorption, transmittance and optical constants are investigated using the full potential-linearized augmented plane wave method with the generalized gradient approximation and mBJ approximation, implemented in Wien2k package. With the mBJ approximation the direct optical gap of a pure ZnO is about 3.34 eV, which is in good agreement with experimental results. The behavior of the transmittance and the absorption of the Al-doped ZnO are higher and better than those of the Si-doped ZnO. The transmittance of Al-doped ZnO is stable and high in the visible light range and can reach 96 % at 400 nm. This confirms the physical characteristics that can present Al to be used as suitable transparent material electrodes in solar cells.